1. Field of the Invention
The present invention relates to an engine generator capable of driving two kinds of generators, an outer rotor type generator and an inner rotor type generator with a common engine.
2. Discussion of related art
Generally, small utility engines have no external electric power sources like batteries. Many of those engines introduce a flywheel magneto type ignition device. The flywheel magneto type ignition device includes a magnet attached to the outer periphery of a flywheel mounted on a crankshaft and an ignition coil attached to a crankcase in a position opposite to the magnet with a specified gap.
Since the angular position of the magnet with respect to the ignition coil is important in determining the ignition timing of an engine, the crankshaft is key-fitted to the flywheel so as to obtain a specified ignition angle.
In the engine generator incorporating such a small engine, the crankshaft is connected to a rotor of the generator to generate electromotive force on a stator side of the generator by rotating the rotor.
An AVR (Automatic Voltage Regulator) method using a capacitor and the like has been widely introduced for a method of controlling the voltage generated by the generator. However, in recent years, the engine generators are required to have a high precision of the voltage stability and the frequency characteristic. In order to meet the requirements, an inverter method in which the generated voltage is outputted as alternating current having a required frequency after being converted into direct currency, is becoming dominant.
Further, generally, an inner rotor type is widely used in the AVR type generators and an outer rotor type is mainly adopted into the inverter type generators.
Accordingly, hereinafter, the AVR type engine generators will be referred to as a conventional type engine generator and the engine generators using the inverters will be referred to as an inverter type engine generator.
Japanese Patent Application No. Toku-Kai-Hei 11-200861 discloses an inverter type engine generator in which a crankshaft is directly press-fitted to a boss of a flywheel through a woodruff key in a locating condition and the flywheel serves also as an outer rotor.
The conventional type engine generator is inexpensive compared to the inverter type engine generator and are still popular with many users. Therefore, in the assembly line, it is convenient that any type of engine generators, conventional type, inverter type, can be assembled whenever necessary, using common engines and housings.
For example, Japanese Patent Application Laid-open No. Toku-Kai 2002-309953 discloses a technique in which the common use of engines and housings is realized by connecting a flywheel with generators having different control methods through an adapter.
The problem of this technique is that the use of the adapter increases the number of components and inhibits the realization of a compact engine generator due to the elongated length in an axial direction.
Further, there is another problem that since a rotor of the generator is secured to the adapter, an outer rotor can not be adopted and therefore the range of applications is restricted.
Further, in case where the woodruff key is used for locating the angular direction of the flywheel with respect to the crankshaft, since the key extends long in an axial direction, the space for fitting the flywheel over the crankshaft is needed to some extent, this inhibiting the realization of a compactly sized engine generator.